This disclosure relates to magnetic compositions for printing and, more specifically, to compositions having magnetic imaging character recognition capabilities.
Magnetic printing methods employ inks or toners containing magnetic particles. Various magnetic inks and toners have been used in printing digits, characters, or artistic designs, on checks, bank notes or currency. The magnetic inks used for these processes may contain, for example, magnetic particles, such as magnetite in a fluid medium, and a magnetic coating of ferric oxide, chromium dioxide, or similar materials dispersed in a vehicle including binders and plasticizers.
In situations requiring magnetic ink character recognition (“MICR”) capabilities, the ink or toner selected should contain magnetic particles having a high level of remanence or retentivity. Retentivity is a measure of the magnetism remaining when the magnetic particle is removed from the magnetic field, i.e., the residual magnetism. When characters printed using an ink or toner having a sufficiently high retentivity are read, the magnetic particles produce a measurable signal that can vary in proportion to the amount of material deposited on the document being generated.
Acicular magnetite is one type of magnetic particle that, due to its retentivity and needle shape, has been used in magnetic inks and toners. For example, U.S. Pat. No. 3,998,160, the entire disclosure of which is incorporated by reference herein, discloses an ink that includes shaped magnetic particles which are subjected to a magnetic aligning process while the ink is on a carrier in a wet state, thereby permitting the authenticity of the printing to be verified. Unfortunately, magnetite particles typically need to be processed or modified to enhance magnetic properties such as retentivity. The additional processing adds cost, time, and material to the process for making the ink or toner composition.
It would be advantageous to provide magnetic inks and toners that provide a number of advantages, including, for example, advantageous processing times.